IMAGINE A PAIR of running shoes that grow spikes on their soles to gain traction when it starts to rain in the middle of a run, or camouflage material that
changes color as the light changes.
Those are just some of the applications
that might become possible with a new
technique known as 4D printing.
The concept starts with additive
manufacturing (3D printing), in which
a machine builds a three-dimensional
object by depositing successive layers
of a material—polymers, resins, metals, ceramics—in almost any shape a
designer can imagine. 3D printing has
been garnering headlines and gaining a foothold in the world of manufacturing in recent years. The industry
analysis firm Wohlers Associates says
the worldwide market for 3D printing
products and services reached $2.2 billion in 2012. Now some researchers are
taking the next step by adding a fourth
“We want to be able to print ob-
jects, products, materials that trans-
form over time,” says Skylar Tibbits,
a research scientist who runs MIT’s
Self-Assembly Lab in Cambridge, MA.
“Why can’t we print dynamic things, or
The idea is to build an object out of
multiple materials using a 3D printer.
The materials would have different
properties—their stiffness, say, or their
sensitivity to temperature or mois-
ture. For instance, one material might
shrink a lot when heated, while anoth-
er would not. By placing those different
materials in the right configuration, a
designer could determine what shape
the object would take when heated.
The idea of materials that change
their shape in response to some stimu-
lus is not unique to 4D printing; other
researchers have worked on “program-
mable matter,” such as thin sheets of
solar cells that can unfold in response
to a temperature change. Combining
that idea with 3D printing, though,
marries the usefulness of active mate-
rials to the new approaches to manu-
facturing provided by the printers.
For instance, being able to print
something in one form and having it
open up into another makes it possible
to print objects that are larger than the
3D printers. Also, printing something
in a compact form could involve less
wasted material, and take less time,
than printing it in its final shape. If an
active object can be printed in a single
piece, without having to screw in or glue
on additional components, it should be
cheaper and quicker to build and have
fewer possible ways to break. “The more
components you have, the more failure-
prone your system is,” Tibbits explains.
In one demonstration, Tibbits print-
ed a black polymer into a flat disk. He
then added to one side of the disk four
concentric rings of a silver-colored
polymer. Halfway between each pair of
rings, but on the opposite side of the
disk, he placed more rings of the same
silvery polymer. When he immersed the
disk in water, it bent along the rings,
upward where the rings were on top
and downward where they were on the
bottom, in accordion-like pleats, form-
ing a ridged, saddle-shaped object.
He also made a series of joined
squares, with ridges where they inter-
sect; when he wets that, it folds along
the ridges into a cube.
Time for a Change
4D printing combines the dimension of time with
the hope of building objects with new capabilities.
Technology | DOI: 10.1145/2601075 Neil Savage
Above, a basic depiction of how a 3D printed object that changes shape or self-assembles
over time becomes a 4D printed object. Below, one of Skylar Tibbits’ 4D objects; this 3D
printed “self-folding straw” starts out as a cable-like structure, but it assembles itself into
a pre-programmed shape when it encounters water.